


“evolution,” bruce agrees

by neville



Category: Marvel Cinematic Universe, The Avengers (Marvel Movies)
Genre: Cute, Domestic Fluff, Early Mornings, Established Relationship, Fluff, M/M, Teaching, Tooth-Rotting Fluff, bruce banner explaining some random science, theyre cutie patooties, this is what i did high school science for
Language: English
Status: Completed
Published: 2019-07-31
Updated: 2019-07-31
Packaged: 2020-07-28 05:13:22
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,097
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20058574
Author URL: https://archiveofourown.org/users/neville/pseuds/neville
Summary: One morning, Bucky asks Bruce to teach him something.prompt #1: early mornings





	“evolution,” bruce agrees

**Author's Note:**

> okay, so, i know, rarepair, but - bear with me because you don't have all the facts
> 
> which are
> 
> i love them
> 
> pls love them too

It’s not often that Bruce is awake this early in the morning; well, really, he is, but his idea of  _ early _ is the small hours he keeps when he’s obsessed with a project, meaning that he wakes sometime after nine and never really gets to see the sun rise.

Bucky doesn’t mind. He exercises first thing, runs around the block and lifts a couple weights, and by the time he’s done Bruce is blearily reading the newspaper and making toast and it’s almost ten. Bruce lectures most days; on those that he doesn’t, he’s working on a top secret S.H.I.E.L.D. project that Bucky isn’t supposed to know about, but he’s figured it out himself that Bruce is trying to find a way to detect extraterrestrial threat at a greater level. Sometimes Bucky catches him wearing a NASA t-shirt, and chuckles  _ nerd _ into Bruce’s shoulder. After breakfast, Bucky goes and tries to save the day, or the month, or the world, depending on the severity of the situation, and then at the end of the day he’ll crash into bed at the same time as Bruce and sling an arm around him. 

“Good night,” he’ll murmur, and then they’ll sleep, and this is their usual routine. 

So it’s a little strange for Bruce to be awake here at six: but it’s one of those Sundays that he can tell will feel longer than they have any right to be, and sunlight is already streaming through their curtains. He sighs gently, knowing already that there’s absolutely no way he’s getting back to sleep now, and he’s about to get up when he realises that Bucky is awake next to him, looking at him with eyes tired in a way that isn’t just from lack of sleep. Bruce touches Bucky’s cheek, slowly, preciously. 

“Teach me something,” Bucky murmurs, closing his eyes and leaning into the touch. This is something they’re still learning; physical intimacy doesn’t come easily or naturally to either, and so they’re trying this together, touching when and however they want to and pushing their ill-drawn boundaries out. Bucky said one night he felt that it helped him when he was feeling low or overwhelmed, and Bruce still thinks about those words and the small smile on Bucky’s face when he’d said them. 

“What do you want to learn about?” Bruce asks. 

Bucky hums. “How about biology?” 

“There’s a lot of things to learn in biology.” 

“Just tell me about anything. Please.” Bucky touches Bruce’s hand, and Bruce hums again, letting his mind drift over years and years of education: postgraduate, bachelor’s, high school, middle school. Bucky winds his fingers in with Bruce’s, and Bruce can feel the tension in his knuckles; he soothes his thumb over Bucky’s hand. Most of their sex isn’t the act itself: it’s easing the tension in their bodies and a little from in their minds, squeezed hands on shoulders and stroked circles onto backs. Nobody has ever done that sort of thing for Bucky before, but Bruce  _ understands _ in a way that other people don’t. 

“How about evolution?” Bucky doesn’t respond, but he shuts his eyes, so Bruce decides to continue. “You know, bacteria can just exchange genetic information horizontally. Isn’t that crazy? Not only can they reproduce asexually, they can just pass their genetics across. They can adapt, and fast - bacteria reproduce quickly - and of course everybody is scared of that because it means we’ve got ultra-resistant bacteria and diseases we can’t treat, but if you think about it, the process behind that resistance is kind of incredible. It takes so many hundreds of years for species to evolve, and bacteria can do it like  _ that _ .” Bruce has been talking so fervently up to the ceiling that he’s forgotten the sensation of Bucky’s presence in the bed, but he’s reminded when he feels the weight shift and Bucky kiss into the soft skin of his neck. Light is filtering through the curtains and daubing their room in the odd shapes of the curtain design. Bruce takes a breath. 

“Evolution is the process by which living things  _ change _ over time through genetic variation; so, we’ve got to have some sort of reason why we see new mutations spread. Take selection. That’s a non-random process where there’s an increase in the frequency of DNA sequences that improve survival, and a reduction in the frequency of deleterious sequences. We get more of the advantageous sequences, because - well, you’re more likely to die if you have the disadvantaged sequence. Selection can favour extreme traits, or the extreme ends of a particular trait, or even just an intermediate of a trait. Whatever it is that helps keep you alive.”

Bucky traces a shape onto Bruce’s chest. “Keep going.” 

“Selection breeds out the bad traits, essentially, and prioritises the good ones. It’s one of the factors involved in the creation of a new species.” Bruce doesn’t even notice that his free hand is drawing invisible diagrams in the air: he’s busy thinking, explaining, sifting through his knowledge and trying to keep it accessible. Bucky would probably sit and listen to him talk in French just for the sound of his voice cutting through the silence, but Bruce wants him to follow. “Speciation – the process of creating a new species – involves isolation, mutation, and selection. Populations become isolated – maybe geographically, or ecologically, or behaviourally. But once the population has been separated into two isolated groups, different mutations start in those groups. Take a population that’s been geographically isolated: the two new groups are going to have completely different environments to adapt to. They evolve different characteristics in order to survive, and once enough time has passed, they become so different from each other that they wouldn’t be able to breed with each other even if you did reintroduce them. So, different species.” 

“Evolution,” Bucky finishes. 

“Evolution,” Bruce agrees, and laughs. “Did they teach you that in the nineteen forties?”

Bucky lets out a little stream of air, and chuckles. “They sure didn’t.” 

The room seems to light up at that thought as the sun emerges from behind a cloud to brighten through the fabric of their curtains, and Bruce wonders for a moment if they should get up or just lie there forever. He’d be fine with either. Mornings are kind of nice, actually, that hazy little zone of sunrise; Bruce doesn’t see the better side of those, usually. His breathing feels a little lighter. Everything seems a little stiller. Even Bucky, now. 

Bucky hums, and then he says, “teach me some chemistry.” 

**Author's Note:**

> thank u to my friend luna for betaing this ... sorry i ignored some of it but i'm a stubborn git who says fuck grammar rules 
> 
> i rly hope u enjoyed!! pls feel free to yell at me if u love this ship too


End file.
